Vitreous enamelled article



June 3, 1947. G. R. slMMoNs' nl 4 VITREOUS ENAMELLED-ARTICLES Filed-June 6, 1942 /NVENTOE l CRS/MMONS BY /Aw ,E

` Arme Ey Patented June 3, 1947 UNITED STATES PATENT OFFICE VITREOUSENAMELLED ARTICLE Glen R. Simmons, Chicago, Ill., assigner to WesternElectric Company, Incorporated, New York, N. Y., a corporation of NewYork Application June 6, 1942, Serial No. 446,117 i 3 claims. (ci. 11irmThis invention relates to vitreous enamelled articles, and to a methodof making the same.

In the manufacture of vitreous enamelled articles having a ferrous metalbase and particularly in the manufacture of telephone number plates `ofthis type, it may be desirable, in order to obtain a smooth enamel nishfree from discoloration, to use an intermediate coating of s-ome othermaterial than that used for the base. It appears that a ferrous metalsurface does not wet satisfactorily with enamel and, hence, adhesion ispoor, and also that during the enamelling heat treatment, some of theiron present is converted into iron oxide which, mixing with the enamel,tends to discolor the enamel.

An object of the invention is to provide an article having a smooth anddurable coating and anieffective and eflicient method of making` thesame.-

x ,In accordance with one embodiment of this invention, an articlehaving a base of ferrous metal is provided with a coating of aluminumand then heated to cause some of the aluminum to alloy with the ferrousbase and some to oxidize to form a ferrous aluminum surface having analuminum oxide coating. A ceramic enamel is then coated on the articleand the article heated to re the ceramic.

Other objects and advantages will be apparent from the followingdetailed description taken in connection with the following drawings,wherein:

Fig. 1 is a plan view of a telephone dial number plate made inaccordance with the invention and Fig. 2 is an enlarged fragmentarysectional View taken along the line 2-2 0f Fig. 1.

In the drawings, a telephone number plate coated with vitreous enamel inaccordance with one embodiment of this invention is shown. The platecomprises a base 3 of ferrous metal. In preparing this base for avitreous enamel coating B, the base is given a thin coating ofsubstantially Dure aluminum. This coating may be obtained by hot dippingor electroplating or other processes which will produce a thin smoothcoating. A thickness of the aluminum coating ranging from .0002 to .003inch appears to be satisfactory. However, the thickness should be keptas thin as feasible and the precise thickness to be employed dependsprincipally on the extent to which the aluminum can subsequently bereadily alloyed with the ferrous base.

An aluminum oxide coating appears to present ioA However, aluminum has amelting point slightly 2 l over 1200 F., while ordinary vitreousenamellng processes are conducted at temperatures in excess of 1400" F.Obviously, the aluminum would be meltedo during enamelling. Thus, inorder to produce an aluminum oxide surface and at the same time a basewhich will be substantially unaffected bythe heat usedin the enamellingoperation, the aluminum coated ferrous metal plate is heat/edito causethe aluminum toalloy with the ferrous metal `and atthe same time to forman aluminum oxide coating over the alloy layer. i

In practicing this inventiomthe aluminumcoated plateis placed in an`oven and heated to a temperature between 1600 F. and 1900" With a platehaving an aluminum coatingap-` proximately .002 inch thick, excellentresults are obtained by heating to a temperature of 1700" F. andheattreating the plate at that temperature for a .half hour. During tlisheating period, the aluminum alloys with the ironzand at the same timethe` aluminum which does not alloy with the iron is'substantiallycompletely oxidized, thus forming an aluminumcoxide coating `5 overthesurface of the ferrous aluminum alloy coating 4. Since the temperatureat which this oxidation and alloying takes place is below the meltingpoint of iron, it appears that the alloying is a result of atomicaction, the action being greatly increased by the relatively hightemperature.

It appears that one effect of the heat treatment in addition to thosenoted is that a large percentage of the carbon in the ferrous base isdriven off as carbon dioxide and thus, in the subsequent enamellingoperation, bubbling of the enamel surface, which may be due to carbon`be-` Percent Red lead 37.4 Pearl ash 5.6 Sodium nitrate 8.4 Arsenicoxide 5 Flint 38 Borax 5.6

This enamel is used in powder form and is spread over the surface of thearticle to be enamelled.

The enamel covered plate is then heated suiliciently to vitrify' theenamel. With an enamel of the composition described, a temperature ofapproximately 1600 F. appears to give satisfactory results; however,with other enamel compositions, the desirable heat treating temperaturemay be somewhat lower or higher. By this process, a vitreous enamelcoating on a ferrous metal base is obtained, the coating havingexcellent adherence, freedom from discoloration and freedom frombubbling.

With some types of enamel, a further improve-V ment in adherence andfreedom from bubbling may be obtained by coating the aluminum coatedbase with an aqueous solution of sodium silicate prior to the heattreating of the aluminum coated base in which the aluminum alloys withthe base. A wetting agent, such as aerosol or any of the various wettingagents on the market, may be added to the sodium silicate to improve theadherence of the silicate to the aluminum. The

, plate is heated to a temperature above the temperature to which it isto be subsequently heated to re the enamel. This is done to drive offthe water from the sodium silicate, the water being removed to an extentdependent on the temperature used. Thus, with an enamelling temperatureof 1600 F., if a temperature of 1700 F, is used to alloy the aluminumand ferrous base, the water in the sodium silicate will be sucientlyremoved so that no water will be driven off during the subsequentenamelling heat treatment. Were water from the sodium silicate drivenoff during the enamelling, bubbling of the enamel would result.

The sodium silicate forms over the article a thin protective coatingwhich is highly resistant to corrosion and fairly resistant to abrasion.At the same time, it impregnates the aluminum oxide and thereby producesa surface to which the subsequent vitreous enamel coating adheres veryclosely, the contact angle of the enamel on this type of surface beingexceptionally small.

While but two embodiments of this invention have been shown anddescribed, many modications and alterations may be made without de- 4parting from the spirit or scope of the present invention.

What is claimed is:

1. An enamelled article comprising a ferrous metal base, said basehaving a ferrous aluminum surface, said surface having a coating ofaluminum oxide, `a coating of sodium silicate over the aluminum oxidecoating, and a vitreous enamel coating over said sodium silicatecoating. Y

2. A method of making an enamelled article comprising the steps ofcoating a ferrous metal base with aluminum, providing a coating ofsodium silicate over the aluminum, heating the coated base to alloy thealuminum with the iron and to form a surface of aluminum oxide over thealloy and a surface of substantially dehydrated sodium silicate over theoxide, coating said base with a vitreous enamel, and firing to vitrifythe enamel.

3. A method of making an enamelled article which comprises applying anaqueous solution of ,sodium silicate to a ferrous metal base having analuminum coating, heating the article to a high temperature to alloyaluminum with the base material, form aluminum oxide and dehydrate thesodium silicate, coating the article with vitriable enamel, and thenheating the article to a lower temperature to vitrify the enamel.

GLEN R. SIMMONS.

REFERENCES CrrED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Great Britain Mar. 30, 1937

